Forming a metal and foam plastic composite

ABSTRACT

A method of fabricating a metal-clad polymeric part by shaping or forming the metal to the contour of the mold cavity and using heat expandable polymeric foam material to exert the necessary pressure to form the metal in one operation.

United States Paiem, 1 1111 3,768,142

Raczek Ucfr. 30, 1973 4] FORMING A METAL AND FOAM PLASTIC 3,166,8311/1965 Keith 29 421 COMPOSITE 2,744,042 5/1956 Pace 29/421 3,613,49510/1971 Podgursky. 29/421 1 Inventorr Thaddeus Anthony Raczek, 3,390,2146/1968 Woods 264 45 Apalachin, NY.

[73] Assignee: international Business Machines Primary Examiner kichardl Herbst Corporation Armonk Attorney-G. R. Gugger et a1. [22] Filed:Dec. 20, 1971 [21] Appl. No.: 210,065

I [57] ABSTRACT [52] 11.8. Ci 29/421, 72/60, 72/364 A method offabricating a metaLclad polymeric part [Sl] ini. Ci 321d 26/04 byShaping or forming the metal to the contour f the [58] Field of Searchmold cavity and using heat expandable polymeric foam material to exertthe necessary pressure to form [56] References Cited the metal in oneoperation.

UNITED STATES PATENTS 3,340,101 9/1967 Fields, Jr. et a1. 148/115 2Claims, 4 Drawing Figures PATENIEDncI 30 ms FIG. 1

FIG. 2

FIG. 3

FORMING A METAL AND FOAM PLASTIC COMPOSITE BACKGROUND OF THE INVENTIONCYCOLAC IS (a registered trademark of Borg- Warner Corporation) is astructural. foam grad of CYCOLAC brand ABS and is processed by theexpansion casting technique. This thermoplastic is supplied in pelletform and incorporates, as an integral part of the pellet, aheat-sensitive chemical blowing agent that causes expansion andsubsequent conformation of the molten plastic material to contours ofthe mold cavity.

Expansion casting may be defined as the seqential heat- 1 ing andcooling of closed molds containing, for example, CYCOLACiJS. Whenexposed to heat, the built-in blowing agent decomposes emitting an'inertgas that causes the softened pellets to expand and fuse together formingstructurally sound lightweight cellular constructed parts.

In applications where a metal-clad, polymeric composite is desired suchas, for example, a metal-clad polymeric machine cover which provides EMCshielding, the practice has been to employ a two-step operationinvolving two seperate processes wherein the polymeric material ismolded separately and a metal sheet is formed separately and then theyare bonded together to form the metal clad composite. The use of twoseparate processes is not only time consuming and costly but twoseperate operations are required and the dimensional matching of thepolymer and the metal is extremely. difficult to obtain. It wouldbe'much more advantageous to produce the composite partin aone-stepoperation where matching of separate parts is not required. j

SUMMARY OF THE INVENTION The present invention makes it possible toobtain the desired metal-clad polymeric composite in a one-stepoperation by making use of the pressure from the foaming agent to formthe metal sheet to the shape or contour of the mold. The metal must beformable at the processing pressures and temperatures of the foamingmaterial. The metal shaping is obtained by using the zinc aluminum alloyreferred to as superplastic and using an ABS foaming material suchasCYCOLAC IS. The CYCOLACJS can be molded by heating at 550 F. Forminutes, which is the softening temperature of the superplastic alloys.The limiting factor is the pressure necessary to form the metal and thepressure created by the heated polymeric foam material. Adhesion betweenthe metal and polymeric material is obtained by applyingan adhesivelayer to the metal.

The present novel one-step forming method which embodies the use of foamas a forming tool and then provides an end use as an insulator or anacoustic muffler results in a new technology which provides aninexpensive approach to tooling as well as meeting the electricalrequirements of EMC shieldingon external covers and also acousticalbaffling on machines which emit noise, such as printers. The presentmethod may also be used advantageously to produce metal-clad polymericcomposites for uses, such as reinforcing, strengthening, solventresistance and heat conductance. I

It is, then, the primary object of the present invention to provide anovel and improved method for producing a metal-clad polymericcomposite.

. A further object of the present invention is to provide a novel andimproved method for producing a metalclad polymeric composite in oneforming operation.

A still further object of the present invention is to provide a noveland improved method which uses an ABS foaming material and asuperplastic to produce a metal-clad polymeric composite in one formingoperation.

A further object of the present invention is to provide a novel andimproved method which makes use of foam as a forming tool and thenprovides an end use as an insulator or an acoustic muffler.

The foregoing and other objects, features and advantages of theinventionwill .be apparent from the following more particulardescription of preferred embodiments of the invention as illustrated inthe accompanying drawings.

- BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing amold loaded with metalparts, a superplastic sheet and a polymeric foammaterial.

. FIG. 2 is a sectional view showing a mold of FIG. 1

after the forming operation.

' FIGQ 3 is a sectional view showing a mold loaded with a superplasticsheet, a film of adhesive and a polymeric foam material.

FIG. 4 is a sectional view showing the mold of FIG. 3 after the formingoperation to produce the metal-clad polymeric composite.

DESCRIPTION OF PREFERRED EMBODIMENTS 'Superplasticity in metals has beenrecognized for some time and this phenomenon is characterized as havingespecially low values of resistance of deformation and extremely .highplasticity as compared, with other alloys and pure components of asystem. Examples of superplastic alloys, such as zinc-aluminum alloy,

inch thick sheet of super-plastic alloy 12, preferrably zinc-aluminum,was clamped in the moldfto overlie the metal parts. The Borg-WarnerCYCOLAC J S foam material 13 in pellet form was then loaded into thecavity on the opposite side from the superplastic sheet and metal partsand the box mold l 1 was clamped together.

The mold was then heated for 30 minutes at 550 F. by any suitable meanssuch as, for example, a circulating hot air oven which is the simplestand most common method used. Upon heating, the built-in blowing agent inthe foam material decomposes, emitting an inert gas that causes thesoftened pellets to expand and fuse together and at the same timeexerting sufficient pressure on the superplastic sheet 12 to form thesheet around the metal parts 10, as shown in FIG. 2. After the 30 minuteheating cycle, the mold is .allowed to cool gradually from to minutesafter which it may be further cooled by a water shower or spray. Theparts were removed from the mold and since no adhesive was used to bondthe materials, there were two separate parts: the mass of solidpolymeric material 13 and the formed superplastic metal sheet 12 withthe metal parts 10 imbedded therein. The embodiment shown in FIGS. 1 and2 illustrates that a piece of superplastic metal sheet can be formed byusing the CYCOLAC JS ABS foaming material.

The above principle was used in the second embodiment shown in FIGS. 3and 4 to produce a metal-clad polymeric part in one molding operation.In this embodiment the bottom portion of the aluminum box mold 14 isdish-shaped to provide a central cavity 15. As shown in FIG. 3, a sheetof superplastic alloy, 16, such as zinc-aluminum, is clamped in the moldto overlie the cavity 15 along with a 0.005 to 0.010 inch thick film orcoating 17 of a suitable thermoplastic adhesive which is positioned ontop of the superplastic sheet. The Borg-Wagner CYCOLAC JS foam material18 in pellet form was then loaded into the mold on top of the adhesiveand the box mold 14 was together.

The mold was then heated for 30 minutes at 550 F. and, as previouslydescribed, the softened foam pellets expanded and fused together. At thesame time they exerted sufficient pressure on the superplastic sheet 16to form the sheet to the contour of the mold and cavity 15, as shown inFIG. 4. After a cooling cycle, the mold was emptied and since the foammaterial and the superplastic alloy were bonded together by the adhesivecoating 17 there was produced a solid metal-clad polymeric composite.

Superplastic alloys 0.020 and 0.010 inch thick have been formed usingthe above described technique. Other metals which could be used include,for example, wrinkled aluminum and expandable screening. Forapplications such as metal-cladding polymeric covers for EMC shielding,a very thin 0.001 to 0.010 inch thick metal skin could be sufficient.Also, by incorporating suitable blowing agents in the variousthermoplastics, such as a modified polypropylene oxide, materials otherthan ABS could be used in the process.

It will be recognized that a novel and important feature of the presentinvention is that the polymeric material functions as the pressuremedium and, secondly, becomes part of the composite structure toaccomplish the basic objective of obtaining a metal-clad polymericstructure with the polymeric material providing the structural strength.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:

1. A method of forming a superplastic metal sheet which comprises:

providing a mold having a surface formed complementary to the shapedesired to be formed; placing a superplastic metal sheet of the typesuch as zinc-aluminum alloy adjacent said surface;

filling said mold with a heat expandable ABS foaming material; and

heating the mold at a temperature of at least 550 F.

for at least 30 minutes to soften the superplastic sheet and to causethe foaming material to expand and exert pressure against said sheet andsurface to form the sheet to the desired shape.

2. A method for producing a metal-clad polymeric composite whichcomprises:

providing a mold having a surface formed complementary to the shapedesired to be formed; placing a superplastic metal sheet of the typesuch as zinc-aluminum alloy adjacent said surface; providing a coatingof thermoplastic adhesive on said metal sheet; filling said mold with aheat expandable ABS foaming material; and heating the mold at atemperature of at least 550 F. for at least 30 minutes to soften thesuperplastic sheet and to cause the foam material to expand and exertpressure against said adhesive coating and sheet whereby the foammaterial and metal sheet are bonded together and formed to the desiredshape.

2. A method for producing a metal-clad polymeric composite whichcomprises: providing a mold having a surface formed complementary to theshape desired to be formed; placing a superplastic metal sheet of thetype such as zinc-aluminum alloy adjacent said surface; providing acoating of thermoplastic adhesive on said metal sheet; filling said moldwith a heat expandable ABS foaming material; and heating the mold at atemperature of at least 550* F. for at least 30 minutes to soften thesuperplastic sheet and to cause the foam material to expand and exertpressure against said adhesive coating and sheet whereby the foammaterial and metal sheet are bonded together and formed to the desiredshape.